This invention relates to an antenna for use in a mobile communication apparatus such as a mobile telephone set and, in particular, to an antenna in which an antenna base element arranged in an antenna top has a flexible structure.
As conventional antenna of the type, use is typically made of a helical antenna and a separate antenna comprising the helical antenna. For example, the helical antenna is manufactured in the following manner. At first, an antenna base element is prepared which has one-end portion provided with a helical coil guide made of a nonconductive material and the other-end portion coupled to a sleeve made of a conductive material. The sleeve has a sleeve-helical coupling portion and a flange portion and serves as a feeding portion. Then, a helical antenna element having an antenna function is screwed onto the helical coil guide and is brought into contact with the flange portion of the sleeve so as to be electrically fed from the sleeve. Finally, in order to protect the helical antenna element and to improve a commercial value in design, an antenna top is molded to cover the one-end portion of the antenna base element and the flange portion of the sleeve.
By the use of the above-mentioned antenna base element, the separate antenna is manufactured. Specifically, a whip antenna element is mechanically fixed to the other-end portion of the antenna base element before the above-mentioned antenna top is molded. More in detail, the whip antenna element is supported at its one end by an insulator forming a body of the antenna base element and extending through an inner bore of the sleeve. The helical antenna element is screwed onto the helical coil guide and is brought into contact with the flange portion of the sleeve so as to be electrically fed from the sleeve. Thereafter, the antenna top is molded to cover the one-end portion of the antenna base element and the flange portion. Subsequently, the whip antenna element is covered with a face tube for protection and smart appearance. Around the face tube, a holder is attached so as to be slidable on the outer peripheral surface of the face tube. A stopper is attached to the whip antenna element at the other end thereof opposite to the one end fixed to the insulator.
Upon manufacture of the helical antenna or the separate antenna described above, it is required to screw the helical antenna element of a predetermined diameter onto the helical coil guide. During any operation in the overall manufacturing process up to the formation of the antenna top, the helical antenna element may be deformed or displaced under some external force. In this event, antenna characteristics will be adversely affected.
In order to avoid the above-mentioned situation, the size of each of the helical antenna element and the helical coil guide is accurately selected so that the helical antenna element is exactly fitted to the helical coil guide to be prevented from easy movement out of its proper position.
However, in order to fit the helical antenna element of such a size accurately selected as described above to the helical coil guide, delicate and skillful work is required. In addition, it is difficult to completely prevent the deformation or the displacement of the helical antenna element. As a result, the production cost is inevitably increased in order to provide good products which are excellent in antenna characteristics and high in reliability.
For example, existing techniques related to the helical antenna and the separate antenna are disclosed in Japanese Unexamined Patent Publications (JP-A) Nos. 5-243829 (243829/1993) and 7-99404 (99404/1995).
It is an object of the present invention to provide an antenna which can be easily and economically manufactured and highly reliable without deformation and displacement during manufacture.
Other objects of the present invention will become clear as the description proceeds.
An antenna to which the present invention is applicable is for use in a mobile communication apparatus and comprises a helical antenna element of a helical shape and a flexible substrate rounded to form a cylindrical shape. The helical antenna element comprises a plurality of oblique conductive patterns extending along the flexible substrate and electrically connected to one another at their terminal ends to form the helical shape. The oblique conductive patterns have a pitch similar pitch therebetween.
It may be arranged that the flexible substrate has end portions facing to each other in the cylindrical shape, each of the oblique conductive patterns extending between the end portions.
It may be arranged that the oblique conductive patterns are parallel to one another.
It may be arranged that the oblique conductive patterns have a width similar to one another.
It may be arranged that the antenna further comprises an antenna top containing the flexible substrate of the cylindrical shape.
It may be arranged that the antenna further comprises a conductive sleeve fitted as a feeding portion to the flexible substrate of the cylindrical shape.
It may be arranged that the flexible substrate has a feeding contact formed on one of two remaining sides thereof to be electrically connected to the sleeve.
It may be arranged that the helical antenna element further comprises a plurality of contact pin terminals connected to first ends of the oblique conductive patterns and a plurality of contact receptacle terminals connected to second ends of the oblique conductive patterns, the contact pin terminals and the contact receptacle terminals being connected to each other in one-to-one correspondence.